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Comment by ddingus | Hacker News Reader

Yes. We had a family incident a number of years back. Stuck on a mountain pass in the cold for the better part of a day. We've also seen a breakdown in the desert, and that one was a couple days.

We always refuel before entering a risky part of travel. Never count on getting there. Make sure. And in a scenario like this that refuel could provide a days worth of heat, depending. No matter what, it's a lot more heat than driving at reduced capacity would have yielded.

Rough metric is you get 1 hour of engine idle per gallon. Some cars do better than that. And you can pulse it, warm vehicle up, make sure everything gets charged, fluids able to flow, etc... and then shut down for 1/2 hour or so in order to stretch the resource.

We carry:

-2 gallons of water

-Car road trouble kit, flairs, compressor, various tools, tape, things...

-First Aid

-Some food

And this is usually our road munchies, pet food, etc...

-Weather related stuff

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> Rough metric is you get 1 hour of engine idle per gallon.

From personal experience that seems extremely conservative, although that may be the point. According to [1], a semi truck or city bus use a little less than a gallon per hour idling.

[1] https://www.energy.gov/eere/vehicles/fact-861-february-23-20...

It's totally the point. For a more precise data, I know my Ford Expedition and Chev Suburban both use about 1/2 gallon per hour, and my Honda is about 1/3.

But, when planning like this it pays to be ultra conservative. Shit happens.

Diesels use less fuel when idling.

How much? I have almost no experience with them.

A ton less.

Basically it has to do with a diesel throttling the fuel and never having any restriction on the air vs a gas engine throttling the air.

Thanks. Interesting. I understand why people get those little diesel heaters, generators.

>Rough metric is you get 1 hour of engine idle per gallon. Some cars do better than that.

I have a non-plug in hybrid, that gets almost 50 mpg consistently; I've got to experiment and extrapolate to see if it's much better. I would like to believe so.

I recently learned of the existence of:

https://en.wikipedia.org/wiki/Gasoline_heater

and wonder how efficient they are.

These seem to be mostly outdated, but I guess that they are particularly useful with air cooled engines, where a conventional heating system doesn't have coolant to work with.

You can buy diesel heaters for caravans, they seem to use about 0.6-0.7 litres/hour (eg. this sort of thing: https://www.amazon.com/dp/B07K1JJ92S/ ).

Can you even idle all hybrids? Doesn't the engine shutoff when stopped? Maybe it will turn on if the coolant temperature drops?

That's the point.

Mine does shut off, if the vehicle isn't moving and the interior temperature matches the climate control setting.

So I would think/hope it could use a fraction of the fuel by running intermittently.

It's gonna be. My normal non / hybrid Honda uses about 1/3 gallon per hour.

A Honda Civic with a D17A1 engine, at idle, with all accessories off, at 700-720RPM, reports 0.6-0.7L/h, or 0.17-0.19 Gal/h over OBD-II. Vent Fan to Full and Mixer to Hot without A/C reports 0.9-1.0L/h, or 0.24-0.26 Gal/h.

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